$ { {0} \times \left[\begin{array}{rr}{0} & {0} \\ {4} & {-1} \\ {0} & {4}\end{array}\right] = {?} } $
Solution: To multiply a matrix by a number, multiply each item of the matrix by the number. ${\left[\begin{array}{rr}{0}\times{0} & {0}\times{0} \\ {0}\times{4} & {0}\times{-1} \\ {0}\times{0} & {0}\times{4}\end{array}\right]}$ Now, simplify: ${\left[\begin{array}{rr}{0} & {0} \\ {0} & {0} \\ {0} & {0}\end{array}\right]}$